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2 Jul 2012

Volume 101, Issue 1, Articles (01xxxx)

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Appl. Phys. Lett. 101, 013701 (2012); http://dx.doi.org/10.1063/1.4730945 (5 pages)

Frederick Gertz, Rustam Azimov, and Alexander Khitun
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Effective work functions for the evaporated metal/organic semiconductor contacts from in-situ diode flatband potential measurements

Mi Zhou, Rui-Qi Png, Siong-Hee Khong, Sankaran Sivaramakrishnan, Li-Hong Zhao, Lay-Lay Chua, Richard H. Friend, and Peter K. H. Ho

Appl. Phys. Lett. 101, 013501 (2012); http://dx.doi.org/10.1063/1.4728121 (4 pages) | Cited 1 time

Online Publication Date: 2 July 2012

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The diode built-in potentials (Vbi) of several polymer organic semiconductor (OSC) thin films [(2,5-dialkoxy-substituted poly(p-phenylenevinylene), poly(9,9-dialkylfluorene), poly(9,9-dialkylfluorene-alt-phenylene(N-phenyl)iminophenylene), and poly(9,9-dialkylfluorene-alt-benzothiadiazole)] sandwiched between p-doped poly(3,4-ethylenedioxythiophene) (PEDT:PSSH) and evaporated metal contacts have been measured by bias-dependent electromodulated absorption (EA) spectroscopy of the Stark-shifted π–π* band. From these values and the vacuum-level offsets at the PEDT:PSSH contacts evaluated by sub-gap EA spectroscopy, the following effective work functions for the buried evaporated metal contacts have been obtained: Al 3.4 ± 0.1, Ag 3.7 ± 0.1, Au 4.4 ± 0.1, and Ca 2.4 ± 0.1 eV. These work functions are smaller than those of the “clean” metal surfaces by up to 0.8 eV, and are substantially independent of the OSC in the absence of charge transfer.
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85.30.Kk Junction diodes
85.40.Sz Deposition technology

Radio frequency signal detection by ballistic transport in Y-shaped graphene nanoribbons

G. Deligeorgis, F. Coccetti, G. Konstantinidis, and R. Plana

Appl. Phys. Lett. 101, 013502 (2012); http://dx.doi.org/10.1063/1.4732792 (3 pages)

Online Publication Date: 5 July 2012

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We report on the fabrication and room temperature measurements of a high frequency electrical signal detector. The device is based on the ballistic transport in graphene to detect a high frequency signal. The observed response is linear in the considered power range (−40 dBm–0 dBm) and exhibits a sensitivity as high as 10 V/W. Finally, the device detected signals up to 50 GHz with a maximum response at 10 GHz. This device outperforms any previously reported carbon based detectors in frequency response and compares to current state of the art Schottky based detectors in dynamic range.
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84.40.Ua Telecommunications: signal transmission and processing; communication satellites
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
72.80.Vp Electronic transport in graphene
72.20.Ht High-field and nonlinear effects

Reduction of threshold voltage fluctuation in field-effect transistors by controlling individual dopant position

Masahiro Hori, Keigo Taira, Akira Komatsubara, Kuninori Kumagai, Yukinori Ono, Takashi Tanii, Tetsuo Endoh, and Takahiro Shinada

Appl. Phys. Lett. 101, 013503 (2012); http://dx.doi.org/10.1063/1.4733289 (3 pages) | Cited 1 time

Online Publication Date: 5 July 2012

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To investigate the impact of only the dopant position on threshold voltage (Vth) in nanoscale field-effect transistors, we fabricated transistors with ordered dopant arrays and conventional random channel doping. Electrical measurements revealed that device performance could be enhanced by controlling the dopant position alone, despite varying dopant number according to a Poisson distribution. Furthermore, device-to-device fluctuations in Vth could be suppressed by implanting a heavier ion such as arsenic owing to the reduction of the projected ion struggling. The results of our study highlight potential improvements in device performance by controlling individual dopant positions.
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85.30.Tv Field effect devices

Potential distribution in channel of thin-film transistors

Koshi Okamura and Horst Hahn

Appl. Phys. Lett. 101, 013504 (2012); http://dx.doi.org/10.1063/1.4733290 (5 pages)

Online Publication Date: 6 July 2012

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Channel voltages of ZnO thin-film transistors during operation are precisely probed at two trisecting positions between the source and drain electrode, which exactly corresponds to characteristic transistor events, such as carrier injection, carrier accumulation, pinch-off formation, and drain current saturation. Furthermore, a simple numerical calculation based on the gradual channel approximation and the current continuity equation reveals that the channel voltages have a non-linear potential distribution and an intrinsic but significant potential drop in the region near to the drain electrode in most of the linear regime.
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85.30.Tv Field effect devices
02.60.Gf Algorithms for functional approximation

A Kondo insulating memristor

D. J. Kim and Z. Fisk

Appl. Phys. Lett. 101, 013505 (2012); http://dx.doi.org/10.1063/1.4733328 (3 pages) | Cited 2 times

Online Publication Date: 6 July 2012

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We report memristor behavior in a macroscopic bulk Kondo insulator Ce3Bi4Pt3 below 10 K. The ac current and voltage relation characteristic of memristors, pinched hysteresis loops which merge into a single line at high frequency, are systematically observed. A standard lock-in technique is used to probe the origin of this exotic behavior which cannot be explained solely by a static resistance drop arising from joule heating. Rather the response appears to be associated with the formation of dynamic thermal impedance in the dissipative regime.
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84.32.Ff Conductors, resistors (including thermistors, varistors, and photoresistors)

Analyses of hetero-interface trapping properties in AlGaN/GaN high electron mobility transistor heterostructures grown on silicon with thick buffer layers

Joseph J. Freedsman, Toshiharu Kubo, and Takashi Egawa

Appl. Phys. Lett. 101, 013506 (2012); http://dx.doi.org/10.1063/1.4733359 (4 pages) | Cited 1 time

Online Publication Date: 6 July 2012

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We report on the analyses of trapping properties of metal-organic chemical vapor deposition grown AlGaN/GaN high-electron-mobility transistor (HEMT) heterostructures on silicon with increasing buffer thickness (Tbuff). An exact exponential dependence of AlGaN/GaN hetero-interface trap time constants with gate bias was observed in the vicinity of threshold voltage. A low hetero-interface state density (Dit) value of ∼2.5 × 1010 cm−2 eV−1 was achieved for heterostructures grown by using thick Tbuff ∼ 5 μm against a Dit value of ∼1 × 1011 cm−2 eV−1 for a similar heterostructures grown with thin Tbuff ∼ 1.25 μm. Further, the high resolution x-ray rocking curve and Van der Pauw-Hall measurements also confirmed that increasing the Tbuff improves the AlGaN/GaN HEMT heterostructures with reduced edge dislocation densities and enhanced carrier transport properties.
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85.30.Tv Field effect devices
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Frequency multiplying oscillator with an electron beam accelerated in a drift space

Kyu-Ha Jang, Kitae Lee, Seong Hee Park, S. Miginsky, and Young Uk Jeong

Appl. Phys. Lett. 101, 013507 (2012); http://dx.doi.org/10.1063/1.4733725 (3 pages)

Online Publication Date: 6 July 2012

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In a uniform acceleration region, the behavior of a velocity-modulated electron beam has been analyzed using a particle-in-cell code. By making use of one of the accelerated harmonic components of the velocity-modulated electron beam, we demonstrate a frequency multiplying oscillator for a compact THz emitter, which employs multiple electron beams and a higher order mode resonator to modulate the electron beam without an additional driving source.
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84.30.Ng Oscillators, pulse generators, and function generators
41.75.Fr Electron and positron beams
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